concurring.
I concur in the principal opinion and in its holding that the Eighth Amendment’s prohibition of cruel and unusual punishments bars the execution of those who were younger than 18 when their crimes were committed.
Both the principal opinion and the dissent strive earnestly to follow relevant precedent of the United States Supreme Court — whether that be the line of reasoning in Atkins v. Virginia, 586 U.S. 304, 122 S.Ct. 2242, 153 L.Ed.2d 335 (2002), or the result in Stanford v. Kentucky, 492 U.S. 361, 109 S.Ct. 2969, 106 L.Ed.2d 306 (1989). That Court’s views may be as divided as this Court’s. The underlying premise of both views is that the constitution forbids the execution of a person who, at the time of the crime, was not fully capable of the kind of adult moral judgment that would hold the offender subject to the death penalty for his crime.
The use of chronological age in making these judgments — as the Court did in Stanford and in Thompson v. Oklahoma, 487 U.S. 815, 108 S.Ct. 2687, 101 L.Ed.2d 702 (1988) — invites the drawing of a bright line as to the age at which a murder defendant may be subject to the death penalty.
The legislature has drawn the line for eligibility for the death penalty at age-15. Section 565.020.2.1 The age 15 standard is consistent with Thompson v. Oklahoma, which held that a child who committed a crime when he was 15 or younger cannot receive the death penalty because of the Eighth Amendment’s proscription of cruel and unusual punishments. Citing evolving standards, the principal opinion here holds that the line is now drawn at age 18.2
What is the nature of this judicial or legislative judgment? When any given age is used, it reflects a judgment that those below that age cannot be fully responsible in terms of being subject to the death penalty. The line is drawn because of the judgment that most if not all persons of such a youthful age are not morally capable of being fully responsible for their acts. This is true even though a child less than 18 may be tried as an adult, found guilty, and receive an adult non-capital sentence. See section 211.071.
The legislature traditionally has drawn lines by chronological age based on assumptions or experience as to maturity.3 There is some judicial authority for defer*416ring to the legislature in this regard even as to capital punishment of those of a certain age, see Thompson v. Oklahoma, 487 U.S. at 854, 108 S.Ct. 2687, 101 L.Ed.2d 702 (1988) (O’Connor, J., concurring) (“I would not substitute our inevitably subjective judgment about the best age at which to draw a line in the capital punishment context for the judgments of the Nation’s legislatures.”). The Thompson decision itself, however, stands for the proposition that line drawing in capital eases is a prerogative of the judiciary in its role of safeguarding Eighth Amendment rights.
Judges have long drawn lines by chronological age. The common law — judge-made law — has had a rich, if somewhat checkered history of recognizing age categories when it comes to criminal responsibility. Under the common law, a child who reached the age of 14 was fully responsible for crimes as an adult. Under the age of seven the common law determined that a person had no criminal capacity. Between the ages of seven and 14, there was a rebuttable presumption that the child lacked capacity to be criminally responsible for the child’s acts. The common law placed the burden on the prosecution to rebut the presumption of incapacity. Rollin M. PeRkins, CRIMINAL Law 887 (2d ed.1969).
The common law, as Perkins has noted, has some grim examples: In the 13th century, a seven-year-old boy was tried for murder; his execution was “pardoned for the king’s sake.” Id. at 838. English records also show that a 13-year-old girl was executed for killing her mistress, a 10-year-old boy was executed for killing a companion, and an eight-year-old boy was similarly punished for “maliciously” burning some barns. Id. Perkins also notes that American records show the execution of two 12-year-old boys for murder. Id. The standards of decency, cited by the United States Supreme Court and by the principal opinion in this case, seem certainly to have evolved. Atkins v. Virginia, 536 U.S. 304, 122 S.Ct. 2242, 153 L.Ed.2d 335 (2002). But evolved how far?
Missouri’s death penalty statute states that the jury, in determining whether or not to recommend the death penalty, can consider “age,” but without elaborating how age is to be considered. Section 565.032.3(7). Despite the lack of elaboration in the statute, the jury is instructed to consider age as a mitigating factor. In this case, in the penalty phase final argument, the defense and the prosecution used Simmons’ age in their arguments. In mitigation, the defense talked about 17-year-olds and their inability to think about the future, and about the fact that a person of 17 cannot vote or lawfully drink alcohol, but can be subject to the death penalty. The prosecutor used Simmons’ age to argue that he should be put to death. The prosecutor’s argument was: “Think about age. Seventeen years old. Isn’t that scary? Doesn’t that scare you? Mitigating? Quite the contrary I submit. Quite the contrary.” The prosecutor seems to have implied that if Simmons was this bad at 17, he could only get worse.
The principal opinion draws a bright line based on the Eighth Amendment’s prohibition of cruel and unusual punishments. However, if the Supreme Court of the United States does not agree with this Court’s conclusion that the standard of decency has evolved to that point, the issue is certainly appropriate for a factual determination on a case-by-case basis. In that event, this Court may wish to take a cue from the statute’s reference to age and borrow the “presumption” concept from the common law.
An updated version would be: A 16 or 17-year-old is presumed not to have the *417capacity to be fully responsible and, therefore, eligible for the death penalty. In the penalty phase, the state could present evidence of the youthful defendant’s full capacity, with the defense entitled to present evidence that the defendant was not fully responsible at the time of the crime so as to be eligible for the death penalty.4 The state would have the burden of overcoming the presumption. The issue of responsibility, in the sense of eligibility for the death penalty, would become the subject of a jury finding, rather than a line drawn by the Court.
Using age as a bright line in juvenile death penalty cases involving 16 and 17 year-olds may be considered unreliable because age, standing alone, is not the true relevant factor as to why it is arguably unjust to impose the death penalty. “Rather, age is simply a ‘proxy’ for a combination of factors such as maturity, judgment, responsibility, and the capability to assess the possible consequences of one’s conduct.” Joseph L. Hoffmann, “On the Perils of Line Drawing: Juveniles and the Death Penalty,” 40 Hastings L.J. 229, 258 (1989). Because age does not correspond perfectly to the combination of relevant factors, its use as a bright line produces “comparative injustice” — that is, some may be spared who are fully capable of receiving the death penalty and others executed who should have been found incapable.
The alternative is the adoption of presumptions with respect to the age of the murderer in capital cases.5 In a case such as this one, where the defendant was a 17-year-old murderer, the Court could hold that persons below the age of 18 are presumed to lack sufficient maturity to be eligible for the death penalty. This presumption would be subject to rebuttal by the state, in which case the unusually mature 17-year-old murderer could receive the death penalty. Proof of such capacity should be beyond a reasonable doubt.6
*418Individualized treatment in juvenile death penalty cases would preserve the capital sentencing option while eliminating or diminishing the comparative injustice problem associated with line-drawing governed solely according to a defendant’s age.
If the Supreme Court of the United States does not agree that age 18 is where the line now should be drawn, the presumption suggested here should be adopted. This would not be based on the Eighth Amendment’s ban on cruel and unusual punishments, but rather a state-law interpretation of the statute that makes “age” a factor in capital sentencing.7
Requiring a specific jury finding on the youthful murderer’s capacity would be consistent with this Court’s over-all duty to ensure that a person lacking full capacity at the time of the crime not be subject to the death penalty.8
This alternative should be used only if the Eighth Amendment’s prohibition of cruel and unusual punishments is held not to bar execution of those who were younger than 18 when they committed their crimes. Because I believe the constitution does bar such executions, I concur in the principal opinion.
. All references are to RSMo 2000 unless otherwise indicated. Section 565.020.2 provides that the death penalty may not be applied where the defendant "has not reached his sixteenth birthday at the time of the commission of the crime.”
. In Brennan v. State, 754 So.2d 1 (Fla.1999), where the Florida Supreme Court held that 16-year-old defendants may not be subjected to the death penalty, Judge Anstead, specially concurring, wrote, "[sjomeone must draw these important lines, and in our unique framework of sharing governmental powers, this function of constitutional line-drawing has been assigned to the judicial branch.” Id. at 12 n. 15 (citing Thompson v. Ok., 487 U.S. 815, 840, 108 S.Ct. 2687, 101 L.Ed.2d 702 (1988)). Judge Anstead was aware of the arbitrariness that could result from such line drawing: "Inevitably, there will be cases where one day’s difference in age will be the determinative factor between life and death.” Id.
.See section 311.325 (setting the minimum drinking age at 21); section 115.133 (setting the minimum voting age at 18); section 431.061 (consent to surgical or medical treatment); section 431.056 (minors’ capacity to enter into contracts); section 451.090 (minors' capacity to enter into marriage contract); section 302.060 (age one can obtain a driving license); section 474.310 (must be 18 to make a will); and section 494.425 (must be 21 to serve on a jury).
. Courts often make decisions regarding the capacity of juveniles. For example, in certifying a juvenile to be tried as an adult, the youth’s age, maturity and sophistication are considered. State v. Thomas, 70 S.W.3d 496, 501 (Mo.App.2002); section 211.071.6. In Thomas, to evaluate whether the defendant, who was 16 at the time of the crime, should be tried as an adult, the chief juvenile officer prepared a report providing that the defendant " ‘appears to be of low average intelligence, responsive, ... mature ... appears to know the difference between right and wrong ... appears to be sophisticated in his manner of living in that he makes his own decision.’ ” Id. To determine whether the defendant’s capacity warrants the death penalty, evaluations similar to that performed for certification could be used.
. The dissenters in Thompson v. Oklahoma also may well have been open to individualized consideration when deciding whether to subject juvenile offenders to the death penally. Justice Scalia wrote at the beginning of his dissenting opinion that, “[i]f the issue before us today were whether an automatic death penalty for conviction of certain crimes could be extended to individuals younger than 16 when they commit the crimes, thereby preventing individualized consideration of their maturity and moral responsibility, I would accept the plurality’s conclusion that such a practice is opposed by national consensus. ... I might even agree with the plurality’s conclusion if the question were whether a person under 16 when he commits a crime can be deprived of the benefit of a rebuttable presumption that he is not mature and responsible enough to be punished as an adult.” 487 U.S. 815, 859, 108 S.Ct. 2687, 101 L.Ed.2d 702.
.It can be argued that the statutory line that bars execution of offenders who were under age 16 at the time of their offenses contains a presumption that those age 16 and above are eligible for the death penalty. The statutory reference to age, and the jury instruction that age be considered a mitigating factor, would place the burden on the young offender to rebut the statute’s supposed presumption. However, establishing presumptions and burdens is traditionally a judicial function, *418though not exclusively so. In cases involving the death penalty, the judiciary’s prerogative to establish presumptions and to assign the burdens of overcoming presumptions is a necessary part of the courts’ duty to ensure that the death penalty is not wrongly imposed.
. Come to that, the presumption logically could be applied to those under 21. That is, after all, the age at which the legislature deems a person to be mature enough to pass judgment as a juror. Section 494.425. But see, Stanford v. Kentucky, 492 U.S. at 374-377, 109 S.Ct. 2969. However, the presumption against the death penally seems better suited for those ages 16 and 17 them for those over age 18. The justification for the presumption is that the death penalty is not appropriate for most persons of a certain age and, thus, the state should have the burden of showing that the less probable case — that the particular offender is mature enough to be subject to the death penalty- — -is true. If most but not all of those over age 18 are suitable for the death penalty, then a defendant may appropriately have the burden of showing that, in his case, age is a sufficiently mitigating circumstance to avoid the death penalty.
. Another statutory basis for holding persons under the age of 18 ineligible for the death penalty may be found in the duty of this Court to ensure proportionality under section 565.035.3(3) RSMo.2000. This section requires this Court to determine whether "the sentence of death is excessive or disproportionate to the penalty imposed in similar cases, considering both the crime, the strength of the evidence and the defendant." (emphasis added) As the principal opinion’s historical analysis demonstrates, in the last decade the death penalty has rarely been imposed on persons under the age of 18. If the sentence of death for a murderer who is less than 18 years old is compared to other sentences of murderers who were the same age, the likelihood of an under-18 murderer receiving the death penalty approaches the likelihood of being struck by lightning. The death penalty for under-18 offenders would appear to be disproportionate.